Li-ion secondary (rechargeable) batteries are widely used for portable battery applications and may find uses in larger size batteries for stationary and transportation applications. As an example, such a battery includes a lithium metal or lithium alloy containing an anode plate, a non-aqueous lithium ion containing electrolyte and an active cathode comprising LiMO2, where M has been a transition metal such as cobalt or nickel or manganese. During charging of this type of battery, lithium ions are removed from the cathode when the oxidation state of the transition metal component of the cathode increases. Lithium ions are inserted in the cathode during reduction at the cathode when the oxidation state of the transition metal component is lowered. Discharging of the battery involves the reverse oxidation-reduction reactions. These electrochemical cells offer relatively high voltage and high energy density performance. In particular, the composition of the cathode and the method by which it is made affects the cost, performance and utility of these batteries.
Current Li-ion batteries often use lithium cobalt oxide (LiCoO2) based cathode material. Due to the high cost of lithium cobalt oxide and environmental issues concerning cobalt there have been extensive efforts to replace the lithium cobalt oxide with a less expensive material such as lithium manganese oxide (LiMnO2) or lithium nickel oxide (LiNiO2). However, lithium manganese oxide is a much less effective cathode material than lithium cobalt oxide, and lithium nickel oxide decomposes when over ⅔ of the lithium is removed (during charge) from its crystal structure. To stabilize the lithium nickel oxide system, partial elemental substitutions on the nickel sites are proposed but they have proven difficult to prepare with uniformity and low cost.
The preparation of lithium nickel oxide compositions partially doped with other elements is usually done by a ceramic processing technique, where a mixture of the oxide precursors are ground to fine powder and heat treated at elevated temperatures (700°–900° C.) in an oxygen atmosphere. The high-temperature ceramic techniques do not produce satisfactory mixing of the doping elements to provide a uniform distribution of the doped elements in the crystal matrix of the lithium nickel oxide. In addition, the ceramic technique requires multiple grinding and heat treatments to achieve even macroscopic mixing. In most cases the ceramic technique provides domains, which are rich in one element and deficient with respect to the other elements. The heat treatment of lithium nickel oxide also needs to be done in an oxygen or oxygen rich atmosphere.
Experimental lithium nickel oxide cathode materials partially doped with other elements have also been made by aqueous solution and precipitation processes and aqueous solution and drying processes. But these practices have been very slow and required high energy consumption for removal of the water.
It is an object of the present invention to provide a practical and efficient method of making uniformly doped lithium nickel oxide compositions for cathode application in lithium-ion secondary batteries. It is a more general object of this invention to provide a method of making mixed metal oxide crystalline materials of the (M1M2)O2 type where the two or more metallic elements are uniformly (or naturally) distributed in the crystal lattice.